.gitconfig is usually stored in the user.home directory.
I use a different identity to work on projects for Company A and something else for Company B (primarily the name / email). How can I have two different Git configurations so that my check-ins don't go with the name / email?
The .git/config file in a particular clone of a repository is local to that clone. Any settings placed there will only affect actions for that particular project.
(By default, git config modifies .git/config, not ~/.gitconfig - only with --global does it modify the latter.)